1. Field of the Invention
It is suspected that somatic growth which follows the administration of growth hormones in vivo is mediated through a family of mitogenic, insulin-like peptides whose serum concentrations are growth hormone dependent. These polypeptides include somatomedin-C, somatomedin-A, and insulin-like growth factors I and II (IGF-I and IGF-II). IGF-I and IGF-II are single chain serum proteins of 70 and 67 amino acids, respectively, and there is evidence that they are identical to somatomedin-C and somatomedin-A. Although IGF-I and IGF-II can be isolated from human serum, such separation at best provides only limited quantities of the growth factors. It would thus be of great scientific and clinical interest to be able to produce relatively large quantities of the growth factors by recombinant DNA techniques. In order to do so, it is necessary to have DNA sequences which encode for IGF-I and IGF-II. In particular, it would be desirable to derive such DNA sequences from their natural source, i.e., human genetic information (RNA or DNA).
2. Description of the Prior Art
The amino acid sequences for human insulin-like growth factors I and II were first determined by Rinderknecht and Humbel (1978) J. Biol. Chem. 253:2769-2776 and Rinderknecht and Humbel (1978) FEBS. Lett. 89:283-286, respectively. The chemical synthesis of biologically active IGF-I has been reported. Li et al. (1983) Proc. Natl. Acad. Sci. USA 80:2216-2220. See also copending application Ser. No. 487,950, filed Apr. 25, 1983, which discloses the expression of synthetic genes for IGF-I and IGF-II in yeast.